How to Use Colour Standards
The human eye remains the most convenient way in which we can detect colour differences in routine work. Unfortunately it is not good at quantifying these differences, or comparing colours in two separate locations, as sight varies from person to person, the eye can be fooled (e.g. with metameric colours), and the person needs experience. All this leads to errors and wasted time in colour matching.
The only way to overcome these problems is by the use of instrumentation that can quantify colour measurements. Suppliers can then check that they are matching the target specified by the buyer without any bias, without delays due to checking each trial with the buyer, and with less need for extended training of staff. This saves suppliers and buyers, both time and money.
There is one weak link in this system though - the instrument itself. If a fault develops and is not detected, then mismatched colours may be produced, giving rise to complaints, lost time and revenue.
A method of checking the instrument is needed to ensure it is working correctly. For this, stable colour standards are required. CERAM Colour Standards have been proven to be very stable and durable, making them ideal for this type of work.
There are three main ways in which the standards can be used:
1. Regular Checks
If measured regularly, later readings can be compared with the initial measurement to check for any changes. Good instruments will not change significantly over many weeks, and it may take years to see definite changes. While this continues, you can be sure that your instrument is working satisfactorily. If changes do occur, a quick study of the results should indicate what corrective action is needed.
First, check to see if several results are showing changes. Ensure that the temperature in the room has not changed unusually (in common with all strongly coloured materials, the CCSII undergo a reversible change of colour with temperature). If the temperature is normal then there may be a fault in the instrument, and the service engineer should be contacted.
If results have changed on only one standard, re-measure it. If this confirms the result then, either that particular standard has undergone a structural change which affects its results (in which case -subsequent readings may be ignored) or there could be a fault in part of the sensor system. Again, the service engineer should be contacted.
After servicing, differences from the initial readings should generally return to near their original small values.
2. Co-ordination between Companies
For this, a set is required which has been ‘calibrated’ with respect to a master set. This can then be used to tie in results from several suppliers and their end user, and of course with those of other suppliers with a similar set-up.
An example of how well this system can work is the introduction of a Tomato Paste Colour Standard into Europe. Millions of Euros could be lost by growers around the Mediterranean who could not measure the colour of their tomato paste accurately (the colour determines the price). Despite the use of instrumentation, results were much too varied to work efficiently. By producing 1,200 calibrated standards at CERAM, all the instruments could be tied together. This reduced the variation in measurements by a factor of 7 and resulted in greatly improved efficiency.
3. ISO 9000 Quality Control
Under this set of standards a company has to prove that when it is measuring its product, the measurement system is giving results which are traceable to National or International Standards. Our Colour Standards are one of the few stable materials available for colour measurement which can be calibrated to provide such traceability over extended periods.
